States give out billions to businesses and corporations each year in tax breaks to keep them within their borders. But tracking how these tax incentives are spent -- and whether they even work -- has been an incredibly tricky business.

Back in 2000, Good Jobs First, which follows corporate tax subsidies, released a report that looked at 122 audits of state economic development programs in 44 states. What it found was that auditors were having trouble doing their jobs because "they are hampered by lack of data and objectives."

The climate has improved somewhat since then, says the group's president, Greg LeRoy. But it's been a long, state-by-state slog.